CIRCULATION. 479 



except away from the heart. The ventricle is filled and emptied alternately as 

 is the normal heart, the artificial valves replacing the heart-valves, which are 

 often necessarily rendered useless by the introduction of the cannula and are at 

 best less certain in their action than the artificial valve. The changes in the 

 volume of the heart are shown by the movements of a liquid column in a 

 horizontal tube which communicates with the bottle filled with "nutrient" 

 fluid in which the heart is enclosed. 



In the original method of Cyon the ventricle is left in connection with the 

 auricle, the ganglion-cells of the ventricle and the neighboring portions of the 

 auricle being kept intact. This " whole heart " preparation is to be distin- 

 guished from the " apex " preparation of Bowditch, which has also been used 

 in studies of the effects of nutrient solutions on the heart. In Bowditch's 

 " apex " preparation, 1 the ventricle is bound to the cannula by a thread tied at 

 the junction of the upper and middle thirds of the ventricle. By this means 

 the lower two-thirds of the ventricle, which contains no ganglion-cells, is cut 

 off from any physiological connection with the base of the ventricle and a 

 " ganglion-free apex " secured. The isolated " apex " at first stands still, but 

 after from ten to sixty minutes 2 commences to beat again and can then be kept 

 beating for several hours. 



In the use of these various methods certain general precautions should be 

 kept in mind. Special attention should be directed to the difficulty of remov- 

 ing the blood from the capillary fissures in the wall of the frog's heart. 3 A 

 small amount of blood remaining in these passages is frequently a source of 

 error. It should be remembered that, as Cyon 4 pointed out, a change in the 

 nutrient solution is of itself a stimulus to the heart, increasing or diminishing 

 the frequency of contraction and obliging the investigator to wait until the heart 

 has become accustomed to the new solution before making an observation. The 

 heart should, as a rule, be constantly supplied with fresh fluid, as in the natural 

 state. The resistance against which the heart works is also a factor of import- 

 ance. The water with which the solutions are made should be distilled in glass, 

 as the minutest trace of the compounds of heavy metals in non-colloidal solu- 

 tions affects the heart. 5 



Nutrient Solutions. Cyon 6 found that the beat of the extirpated frog's 

 heart is very dependent on the nature of the solution with which the heart is 

 fed. Hearts supplied with normal saline solution (NaCl, 0.6 per cent.) ceased 

 to beat much sooner than those left empty. The serum of dog's blood seemed 

 almost poisonous. Rabbit's serum, on the contrary, postponed the exhaustion 

 of the heart for many hours, provided the limited quantity contained in the 

 apparatus was renewed from time to time. Serum used over and over again 

 caused the beats to lose force after an hour or two. The renewal of the serum 

 seemed a stimulus to the heart, causing it to contract very strongly during a 

 half minute or more, after which the contractions became less energetic. 



1 Bowditch, 1872, p. 139. 2 Merunowicz, 1876, p. 135. 



8 Martius and Kronecker, 1882, p. 547. * Cyon, 1867, p. 89. 



5 Locke, 1895, p. 331 ; Naegeli, 1893, p. 12. Cyon, 1867, p. 89. 



